Sewage treatment process

ABSTRACT

A continuous sewage treatment process for upgrading the quality of sewage plant effluent by converting sewage sludges to active substances and returning these active substances to the sewage system whereby removal of dissolved contaminants occurs by the addition of the active substances.

O Umted States Patent [151 3,640,820

Kemmer et al. 1 Feb. 8, 1972 [54] SEWAGE TREATMENT PROCESS [56] References Cited [72] Inventors: Frank N. Kemrner, La Grange; Reid S. UNITED STATES PATENTS Robertson, Glen Ellyn; Rodney D. Mattix, Lemom, a f[]] 3,440,166 4/1969 Davis et al. ..210/1O X 1,915,240 6/1933 Putnam ....210/7 X 1 Asslgnee= Nalw Chemical Company, Chmgo, 3,345,288 10/1967 Sontheimer... ..210/10 2 Filed: Janll 1971 1,903,834 Oberle [21] Appl. No.: 77,047 Primary Examiner-Michael Rogers Attorney-John G. Premo, Charles W. Connors and Edward Related US. Application Data ptacek 63 Continuation-inart of Ser. No. 852,421, Au 22, l 1 1969. p g [511 ABSTRACT A continuous sewage treatment process for upgrading the [52] [1.8. CI ..2l0/6, 210/ 10, 210/152, quality of sewage p|am effluent by converting Sewage sludges 252/422: to active substances and returning these active substances to [51] f the sewage system whereby removal of dissolved contami- [58] Fleld of Search ..210/3-9, 10, 45, Hams occurs by the addition f the active substances 2Cla1ms' ,lDrawingiigure FEEDER 56 5 I 51:22: AERATION SECONDARY rem'uuzv 2 BASIN CLARIFIER TReA'rM la m 58 26 F 11 1 1 Q1 "EL :r E "E I 74 p P l SECONDARY 22m: 28 3. 34 32 -o 60 VACUUM 76 FlLTER FURNACE OXlOlZlNG mum/1am Fl LTRATE TRANSFER To FEED SYSTEM A DSORBENT SEWAGE TREATMENT PROCESS This is a continuation-in-part of our copending application Ser. No. 852,421 filed Aug. 22, 1969.

INTRODUCTION The disposal of sewage sludges resulting from large-scale sewage treatment plants is a growing problem. Many schemes have been proposed to efficiently dispose of sewage sludges but, by and large, such systems have not been completely satisfactory. Sludge can be disposed of by incineration, which presents one feasible method of disposing of this material. However, the equipment required to effectively incinerate sludge is expensive and, often cannot be justified except in those instances where land fill or other methods of disposal are restricted.

Another proposed solution for effectively disposed of sludge is its conversion into fertilizer. This use of sludge requires elaborate equipment to dry and process the sludge and physically render it sterile and convert it into a form which is acceptable to the horticultural and agricultural industries.

. Other schemes for disposal of sludge such as dumping into bodies of water and its use as land fill presents problems from a pollution standpoint. At the present time many regulatory agencies prohibit the dumping of sludge into bodies of water due to its being a pollutant. In land fill disposal, the sludge must be dried and, in most instances, transported to an area where land is available or where there is a need of organic fill material.

With sewage sludge disposal problems becoming more marked in their severity from both a health and cost standpoint, it would be beneficial if a method were available whereby sludge could be converted into a valuable and useful product having economic value and which would not represent a disposal problem.

Population growth and industrial expansion is forcing a greater reuse of water and causing higher pollution loads. Of particular increasing concern is the increasing levels of organic material, particularly soluble forms, remaining in waste after normal processing through sewage treatment plants. There is a need to provide methods to overcome this by improving the performance of sewage treatment plants. Therefore, it would be of great benefit to the sewage treatment industry if it were possible to convert sludge into a substance which could be used in the sewage treatment process itself to improve its operational characteristics whereby the aqueous effluents from such processes would be rendered less harmful from a disposal standpoint.

If it were possible to convert sewage sludges into a useful water treatment agent, it would provide a great benefit to the sewage treating industry and to the general public.

OBJECTS OF THE INVENTION It is an object of the invention to provide an improved method for handling and treating sewage sludge whereby it is converted into a useful product which may be used in a sewage treatment process, or which may be used as a valuable product of commerce.

It is a further object of this invention to provide an improved sewage treatment process which produces an active substance which, in turn, can be used in the sewage system to remove dissolved contaminants.

A further object of this invention is to produce an active substance by means of a one-step heating mechanism which not only chars the sludges, but also conditions the chars to make the active substance.

Further objects will be apparent in the specifications.

THE INVENTION The present invention is directed to a method of improving sewage treatment processes by converting sewage sludges into a valuable active substance for return to the sewage treatment system. In a specific embo;iment of the invention a method is provided for improving the operational efficiency of sewage treatment plants whereby at least a portion of the sludge produced by such plants is converted into an active substance. At least a portionof this active substance is then used in these plants as a water-treating aid to improve the overall quality of the waste effluent waters produced by such plants mostly by removing soluble pollutants and whereby the sludges may be efficiently disposed of without danger of pollution or other sanitation problems arising.

THE DRAWING With particular references to the drawing, there is shown schematically in oversimplified form a typical sewage treatment plant.

Specifically the plant is composed of a primary clarifier 10 into which raw sewage is fed through line 12. The primary clarifier sludge is separated from the liquid phase of the sewage, with the liquid being passed to an aeration basin 14 through line 16. After the liquid is aerated in the aeration basin, it is moved through line 18 to a secondary clarifier 20 where the additional solids are removed by sedimentation procedures. The supernatant effluent from clarifier 20 passes through line 22 to an optional tertiary treatment zone or stage 24, where any remaining insoluble solids are removed to provide a final effluent which is discharged through line 26.

In the primary clarifier, at least a portion of the soluble organic waste may be converted into a sludge.

An optional step is to include an adsorption column 70 into which the final effluent is discharged through line 26 for removal of soluble solids. The effluent from column 70 is discharged through line 72.

Sludge removed in clarifiers l0 and 20 pass from these units through lines 28 and 30 respectively, and in some cases the fill from an exhausted column 70 from the tertiary treatment, could also be fed to a common feed line 34 where the sludges are combined and then deposited onto vacuum filter 36. The combined sludges are dewatered in vacuum filter 36 and passed into a filter cake storage unit 38, where they are removed by conveyor 40 to a charting and conditioning furnace 42.

A portion of the sludge from line 30 may be recirculated to line 16.

Sludges entering furnace 42 are subjected to heat treatment in a controlled atmosphere with a conditioning agent present during which the residual moisture of the cake is removed and it is converted into the active substance of the invention. The active substance is then removed from furnace 42 through line 44 and transferred through line 46 as a slurry to feeder 48. The active substance is mixed and fed through one or more of a series of supply lines 50, 52, 54, and 56 to a choice of lines l2, 16, 18, 22 and 26 where it is used to improve the clarity and quality of a supernatent effluent leaving any or each of these units. In some plants a single application point may produce the desired results, while in other plants a plurality of addition points may be necessary. In particular, the active substance reduces the soluble solids in the supernatent effluent. The active substance may additionally be used as a filter media for line filters 58 and 60 which service line 18 and the filtrate feedline 62 on the vacuum filter 36, and as the final treatment stage in column 70.

As will be noticed from the drawing, the active substance is made from a variety of sludges entering the vacuum filter 36 from the primary clarifier 10, the secondary clarifier 20, the tertiary treatment 24, and the exhausted adsorption column 70. This invention contemplates using sludge from any of the sources involved in a sewage treatment process.

THE FURNACE The heating treatment in the presence of a conditioning agent produces the active substance of this invention. Heating sewage in a furnace to high temperatures is known in the art as incineration. Heating sewage in a furnace without a conditioning agent produces a waste ash which is disposed of relatively easily, but has no activity in terms of the present invention.

The furnace must be designed to withstand the fumes generated in the heating step. A kiln can also be used as the furnace and not depart from the subject matter of the invention. The temperature of the furnace can range from 300 to 900 C. Preferably, the temperature should be from 500 to 700 C. It has been found that at least three minutes are needed to achieve any sort of significant activation. The time can range from 3 to 200 minutes, depending upon the sludges used and the conditioning agents. The time and temperature can be varied to achieve the best working arrangement. The pressure should be at least one atmosphere absolute. Greater pressures can be used and may be beneficial in some cases. Under the right conditions, a partial vacuum may be used in the practice of this invention.

CONDITIONING AGENTS Conditioning agents are known to the art and can consist of any organic or inorganic compound that are acidic and produce acidic byproducts under the furnace conditions. By way of example, carbonate activating agents can be used. These compounds can be bicarbonate salts, carbonate salts or even carbon dioxide and carbon monoxide under appropriate conditions.

The dosage of the conditioning agents should be from 0.1-50 percent by weight based on the dry weight of the sludges. Preferably, the furnace should contain from 1 percent to 25 percent by weight of the conditioning agents based on the dry weight of the sludges.

THE ACTIVE SUBSTANCES The active substance produced in accordance with the invention is a unique material in that while it usually contains at least 20 percent by weight inorganic material in the form of their oxides or in the form of inorganic salts, it may exceed 60 percent by weight inorganic material. In most instances the inorganic portion of the active substance produced in accordance with the invention will range between 20-50 percent by weight. The inorganics present in the active substances are composed of a variety of oxides and salts, usually metals, with, in most cases, at least 5 percent by weight thereof and in certain instances from -30 percent by weight of the inorganic component being composed of silica, expressed as SiO The inorganic portion of the active substance, using the preferred conditioning agent of the invention, is primarily derived from the inorganic substances normally found in sewage sludges. Typical analyses of sewage sludges obtained from Downers Grove, Illinois, Sewage Treating Plant is presented in the following Table I.

TABLE I Chemical Constituents of Sludges Arno; 0J3 0.0]3 1 a 0.0043 I, 0.00l I no, 2.02 3.09 Ignition Loss 44.4 68.55 Total 95.65 99.90

The balance of the active substances is basically a form of carbon which is derived from the organic portion of the sewage sludges when they are subjected to the charring and conditioning step of the furnace 42 of the drawing.

The active substances of the invention, in addition to being capable of aiding in the removal of suspended solids from sewage treating effluents, have the additional advantage of removing dissolved contaminants, particularly dissolved organic matter. The active substances can be fed into the primary clarifier, the aeration basin, the secondary clarifier and used in tertiary treatment. This tertiary treatment may involve the use of the active substances in a column as a filter bed and adsorption media. The active substances have a high capacity for adsorbing dissolved contaminants. Further, the active substances when combined with sludges in the sewage process aids in settling, reduces bulking, and helps in the dewatering steps by reducing the chemicals required and improving sludge handling characteristics. When the active substances are fed into the respective tanks, the treatment level should be such as to obtain at least 100 p.p.m. during the course of exposure, in order to have a significant effect on the reduction of contaminants present. Preferably, the treatment level should be at least 500 p.p.m. In a preferred embodiment of the invention, the active substance is thoroughly mixed with the influent before entering the tanks to achieve maximum efficiency in the respective tanks.

EXAMPLES To illustrate the fact that the dried sewage sludges are capable of being converted into a useful active substance, the following is presented by way of example.

lmhoff sludge, a partially digested raw sludge, was obtained from the Metropolitan Sanitary District of Greater Chicago and conditioned with an acrylamide coagulant type polymer, filtered and dried.

Test results combined with knowledge of the art indicate that the average plant employing a properly running activated sludge process could be expected to produce sufficient active substance for their own needs. Any excess active substance may be used elsewhere in the plant. For example, the excess could be used to purify stack gases. The excess could be sold for industrial and agricultural uses. The level of recycle of active substance will vary. The scheme presented by this invention may be employed in conjunction with a wide variety of waste disposal plants now in existence. Such plants may be considered as being composed of at least one sludge settling zone, and a sludge dewatering zone. This sludge settling zone may comprise a number of independent units such as primary and secondary clarifiers. The dewatering zone may comprise vacuum filters such as are shown in the drawing and may be in the nature of sludge drying beds or the like.

It is understood that the typical large sewage plants may include other units, such as elutriators, thickeners, digesters, as well as vacuum filters, centrifuges and the like. The sludges may be produced as a result of any conventional sewage treatment process.

Prior to being subjected to the heat treatment portion of the process it is beneficial that the sludges be sufficiently dewatered so that is contains not more than percent by weight of moisture. The active substances produced in accordance with the invention may be used in any or all of the various clarification treatment operations normally performed in sewage treatment plants. Excess active substances may be sold as a commercial product. Preferably the active substance is added to the effluent from the aeration basin. The recycled sludge from the secondary clan'fier returned to the aeration basin would then normally contain the active substance as well as the normal sludge. This may allow the size of the basin needed in the sewage system to be greatly reduced. The active substance can also be used in a tertiary treatment step as a final polish on the effluent.

Under some conditions it may be desirable to include a washing step after the active substance is discharged from the furnace. This washing step would remove soluble contaminants from the substance and allow them to be properly controlled in the sewage treatment system.

The following tables illustrate some of the tests that have been run varying the conditioning agents, the amount of conditioning agent, time of conditioning, and furnace condition.

TABLE I1 Activating Agent Removal TOC CO 24 Dry CO,-Wet Sludge 38 Wet CO Dry Sludge 2 NaHCO,-(2S%) l NaHCO;,-(50%) l NaHCO;,-(50% with Acid Wash) 67 Na,CO;a4-(2S%) l Na,CO,a4-(25% with Acid Wash) l8 Table II shows various carbonate compounds being used as conditioning agents. Carbon dioxide was effective when using a wet sludge. This is probably because an acidic carbon compound is formed. Sodium bicarbonate was effective when followed by an acid wash.

In the above table, the temperature of the furnace was 600 C. The time in the furnace was about 10 minutes at temperature. The pressure was slightly over one atmosphere so as to maintain a positive pressure within the furnace. The moisture of the sludge was about 40percent by weight.

Table III shows the effect of temperature.

TABLE [II Effect of Temperature (Time was 10 minutes) Sample Temp.

No. (C.) Yield Removal TOC l 365 49% 42% 2 500 36% 4l% 3 600 33% 4l% 4 700 b 44% As can be seen from the table, increasing the temperature decreases the yield but increases the removal of total organic carbon. At 365 C., the removal of total organic carbon was a negative value. This indicates that the soluble organic species from the substance added contaminants to the system rather than removing soluble organics from the system.

Table IV shows the effect of time of activation.

As shown by the table, increasing the time beyond a certain point decreases the yield and the removal of total organic carbon.

SUMMARY This invention involves a process of treating sewage so as to form an active substance useful in removing soluble contaminants in the sewage system. By the use of conditioning agent, appropriate temperature and time, an active substance is produced.

We claim:

1. A continuous sewage treatment process, comprising the steps of:

A. removing at least a portion of the sludges from the sewage system;

B. dewatering the sludges such that said sludges contain from about 10 to percent water;

C. heating the dewatered sludges at a temperature of from 300 to 900 C. for from 3 to 200 minutes at a pressure of at least one atmosphere absolute, in a controlled atmosphere, after adding from 0.l to 50 percent, based on the dry weight of the sludges of an acidic carbonate activating agent selected from the group consisting of bicarbonate salts, carbonate salts, CO and CO;

D. removing at least a portion of the sludges which is now active substance; and

E. mixing said active substance in the sewage system so as to achieve a concentration level greater than p.p.m. in the system whereby removal of dissolved organic contaminants occurs by the addition of said active substance.

2, The continuous sewage treatment process of claim 1, which includes the additional step of: washing said active substance with a liquid selected from group consisting of water and dilute acid to remove the soluble components before returning said active substance to the sewage system, so as to achieve a concentration level greater than 100 p.p.m. in the system whereby removal of the dissolved organic contaminants occurs by the addition of said active substances. 

2. The continuous sewage treatment process of claim 1, which includes the additional step of: washing said active substance with a liquid selected from group consisting of water and dilute acid to remove the soluble components before returning said active substance to the sewage system, so as to achieve a concentration level greater than 100 p.p.m. in the system whereby removal of the dissolved organic contaminants occurs by the addition of said active substances. 